Centrifugal classifier



7,1970 C.'E. LAPPLE 3,491,879

'CENTRIFUGAL CLASSIFIER Filed April 18. 196'? 2 Sheets-Sheet 1 INVENTOROHARLE-s E1 LAPPLE ATTORNEYS Jan.- 27, 1970 c. s. LAPPLE CENTRIFUGALCLASSIFIER Filed April 18. 1967 INVENTOR.

Sheets-Sheet 2 ATTORNEYS United States Patent 3,491,879 CENTRIFUGALCLASSIFIER Charles E. Lapple, Los Altos, Calif., assignor to DonaldsonCompany, Inc., Minneapolis, Minn., a corporation of Delaware Filed Apr.18, 1967, Ser. No. 631,628 Int. Cl. B04c 3/00 US. Cl. 209144 ClaimsABSTRACT OF THE DISCLOSURE Apparatus for classifying particles of apowder according to size having a rotor and a stator separated by anarrow annular air gap. The rotor has a hollow coaxial chamber thereinin communication with the air gap along the periphery of the rotor, anda central coaxial opening for the egress of an elutriating fluid and thefine fraction of the powder. The elutriating fiuid under pressure issupplied to the chamber through the gap and a vortex is producedgenerally within the rotor in the flow of fluid by the rotation of therotor. The powder to be classified is supplied to the vortex and thecoarse fraction of the powder, which is forced toward the stator, isremoved through a coarse fraction passageway while the fine fraction isremoved with the fluid through the axial opening in the rotor.

BACKGROUND OF THE INVENTION Field of the invention Powders of variousmaterials are utilized to an ever increasing extent in present daytechnology. In many of various industries that use powder, such aspowdered metallurgy, magnetic tape, abrasives, pigments, etc., certaincharacteristics must be rigidly controlled. In such cases particle sizeis one of the most important properties of powders and governs suchphenomena as flowability, packing density, and physical reactivity. Forthis reason, powders are ordinarily prepared to a given sizespecification by a process which is termed classification.Classification in general is the separation of a powder into a coarsefraction containing coarse particles, having a size somewhat larger thana cut size, and a fine fraction containing fine particles having a sizeequal to or less than the cut size. The cut size is equivalent to theseparation point or the particular size of particles about which thepowder is separated. Although there should be at least some particleshaving a size larger or coarser than cut size and at least someparticles having a size smaller or finer than cut size, it is notnecesary to actually have any particles with a size equal to the cutsize in the powder. Particle size is usually expressed in terms ofparticle diameter. If particles are not spherical, an equivalent orapparent diameter may be used. One common method is to express size interms of an equivalent spherical particle having the same settlingvelocity as the particle in question.

Description of the prior art In most prior art centrifugal separatorsutilizing a rotor, the rotor is spinning within a chamber to form avortex within the chamber and the powder is drawn into the vortex andthe rotor at a continuous rate. The rotation of the rotor forces thelarger particles toward the sides of the chamber while the fineparticles are carried inwardly to a fine fraction outlet. The largerparticles after reaching the sides of the chamber generally drop,through the force of gravity, into a coarse fraction outlet. At normallyfeasible industrial capacities, particle concentrations in the air areso high that it is Virtually impossible to have all the particlesdispersed as discrete par- 3,491,879 Patented Jan. 27, 1970 ICC ticlesat the same time during the entire classification. Because there is nodispersion of the particles prior to introduction thereof to the rotor,the particles have a tendency to form bunches or groups which, becauseof their size, are forced outwardly and egress through the coarsefraction outlet. Thus, fine particles pass into the coarse fraction withthe coarse particles and the sharpness of separation is greatly reduced.

Although prior art centrifugal air separators are capable of separatingfine powders into fine and coarse fractions, the sharpness of separationis usually not good. That is, the dividing line between the fine and thecoarse fractions is not well defined and both groups will have someparticles of the same size therein. This lack of sharpness of theseparation in the centrifugal air separators becomes more pronounced asfiner powders are processed. To provide sharpness of separation in theprior art centrifugal air separators, the powders must be processed manytimes. Also, in order to achieve a very small cut size at reasonable airflow rates, very high separating forces must be exerted on theparticles. Such high forces are usually obtained in rotary centrifugalclassifiers by high speeds of impeller rotation. Because of practicallimitations of either equipment construction or power consumption,conventional air or gas separators are limited as to the smallest cutsize that can be achieved with reasonable gas handling capacities.

SUMMARY OF THE INVENTION This invention pertains to an improved particleclassification device and more specifically to a centrifugal classifierin which the particles of the powder are subjected to succesivedispersion during classification so that, in general, all particles aresubjected to elutriation individually, at some time during theclassification step, and the particles are subjected to a statisticallyuniform elutriation throughout the classification.

In the present device, a rotor is mounted for rotation approximatelyconcentrically within an annular ring so that a small uniform gap isproduced therebetween. The rotor is constructed with a chamber thereinwhich extends radically outwardly to communicate with the gap at theperiphery of the rotor. Also, the rotor has a coaxial opening thereinfor the egress of elutriating fluid and fine particles from the chamberin the rotor. Elutriating fluid, in this embodiment air, is supplied tothe rotor in a manner to provide a fiow through the gap to the coaxialopening in the rotor. Some means are supplied to rotate the rotor at apredetermined uniform speed so that the elutriating fluid is formed intoa vortex as it flows from the gap to the coaxial opening. In the presentembodiment fins or baffles are utilized to aid in forming asubstantially forced vortex, however, it should be understood that thefins might be eliminated and a vortex would be formed in a manner wellknown to those skilled in the art. The powder to be classified isinjected into the vortex and the coarse fraction is removed from thevortex at some point along the annular ring ahead of the powderinjection point relative to the rotation of the rotor. Because thecoarse fraction is removed from the vortex at a point spaced from theinjection of the powder, the particles have a chance to disperse asdiscrete particles through successive dispersion as they rotate aroundthe outer periphery of the chamber in the rotor. Since the particles aredispersed as discrete particles, the aerodynamic characteristics aredirectly related to the size of the particles. In air classifiers, theseparation is determined in terms of the aerodynamic characteristics ofthe particles as they are suspended in the air stream and, consequently,the present air classifier separates the particles according to size.This successive dispersion and separation of the particles according tosize greatly increases the sharpness of separation thereof. Also,because of the improved design of the rotor, the present classifier canefficiently and practically separate powders at cut sizes lower thanpreviously practical.

It is an object of the present invention to provide a new and improvedcentrifugal classifier.

It is a further object of the present invention to provide a centrifugalclassifier capable of separating powders with greatly increasedsharpness.

It is a further object of the present invention to provide a centrifugalclassifier capable of separating powders at greatly reduced cut sizes.

These and other objects of this invention will become apparent to thoseskilled in the art upon consideration of the accompanying specification,claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings, whereinlike characters indicate like parts throughout the figures:

FIGURE 1 is an elevational view of a centrifugal classifier systemconstructed in accordance with the present invention;

FIGURE 2 is a top plan view thereof;

FIGURE 3 is a side elevational view as seen from right to left of FIGURE1;

FIGURE 4 is a sectional view thereof as seen from the line 4-4 of FIGURE1 on an enlarged scale;

FIGURE 5 is an enlarged sectional view thereof as seen from the line 55of FIGURE 6.

FIGURE 6 is a sectional view thereof as seen from the line 66 of FIGURE4 on a reduced scale; and

FIGURE 7 is a sectional view thereof as seen from the line 7-7 of FIGURE4 on a still further reduced scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT The main body of the centrifugalclassifier, generally designated 10, includes a housing 11 and a rotor12. The housing 11 comprises a first flat circular plate 13, a secondflat circular plate 14 having a horizontal base portion 15 fixedlyattached thereto, and an annular ring 16 mounted between the twocircular plates 13 and 14 to form a generally circular cavity 17. Thecircular plates 13 and 14 are connected to the annular ring 16 in anyconvenient manner, such as screws or the like, so that the cavity 17 issubstantially air tight. The second circular plate 14 has a coaxialopening 18 therethrough. The annular ring 16 has a portion 19 whichextends radlally inwardly around the entire circumference of the annularring 16 and has a transverse width somewhat shorter than the remainderof the annular ring 16.

The rotor 12 comprises a pair of similar annular rings fixedly connectedin an axially spaced apart relationship by a plurality of bolts 26having spacers 27 therearound. The outer diameter of the annular ring 251s slightly smaller than the inner diameter of the portion 19 of theannular ring 16 to form a gap 28 therebetween. The annular rings 25 areconstructed with a generally triangularly shaped cross section, and theyare fixed together so that the hypotenuses thereof converge toward theouter periphery. However, the extreme tips of the triangle are truncatedwith the adjacent tips formlng radially extending sides which aremaintained in a parallel spaced apart relationship by the spacers 27.The spaced apart sides of the annular rings 25 form a passageway 29through which the inner opening formed between the annular rings 25 isin communication with the gap 28 around the entire periphery of theannular rings 25. Although the annular rings 25 are triangularly shapedin this embodiment, it should be understood that any shape which willprovide the desired results might be utilized or in some instances theymight be eliminated.

A first circular plate 30 and a second circular plate 31 each have anouter diameter slightly larger than the inner diameter of the annularrings 25. The circular plates 30 and 31 are clamped coaxially over theannular rings 25, by means of a plurality of screws 32, to form a hollowrotor 12 having an annular aperture 01, as in this embodiment, a chamber33 therein. Each of the circular plates 30 and 31 has an annular grooveextending around the outer periphery thereof and adapted to receive theinner periphery of the annular rings 25 therein to render the chamber 33substantially gas tight and to prevent movement between the circularplates 30 and 31 and the annular rings 25. It will be clear to thosskilled in the art that the annular rings 25 can be eliminated asseparate parts and formed integrally with the plates 30 and 31 ifdesired.

The second circular plate 31 in the rotor 12 has a coaxial opening 35therein which is in communication with the coaxial chamber 33. Acylindrical conduit 36 having a radially outwardly extending flange 37adjacent one end thereof, is fixedly connected to the second circularplate 31 coaxially therewith by means of a plurality of screws 38threadedly engaged through the plate 31 and the flange 37. The innerdiameter of the conduit 36 is approximately equal to the diameter of theopening 35 in the plate 31 so that a continuous passageway is formed.The conduit 36 extends axially outwardly from the rotor 12 through theopening 18 in the housing 11. Two bearing means 40 mount the conduit 36,and the attached rotor 12, for rotation about their horizontal axis. Thebearing means 40 are mounted with the base portion 15 of the housing 11by means of a pair of columns 41.

A shaft seal 42 is fixedly attached to the second circular plate 14coaxial with the conduit 36 to maintain the cavity 17 in the housing 11substantially free from the ingress and egress of air. The shaft seal 42includes a member 43 having a generally cup-shaped configuration fixedlyattached to the outer surface of the second circular plate 14 so as toform an annular cavity 44 surrounding the conduit 36 adjacent the outersurface of the second circular plate 14. Substantial quantities of thefluid which is utilized for elutriation in the rotor 12 are forcedthrough the annular cavity 44 so that a strong current of elutriatingfluid is always flowing from the annular cavity 44 inwardly toward thecavity 17 and outwardly into the atmosphere. Since the elutriating fluidis always flowing outwardly in both directions from the annular cavity44, no solid particles can enter the cavity 17 in the housing 11therethrough. A similar type of shaft seal, designated 45, is utilizedat the outer end of the conduit 36 to connect that end to a nonrotatingconduit 46. While the specific shaft seals 42 and 45 have been describedin some detail, it should be understood that they do not form a part ofthis invention and any means which can provide the described functionswill come within the scope of this invention. The nonrotating conduit 46leads to a fine fraction accumulating means 47, illustrated in FIGURE 3,which will be described in more detail presently.

Two passageways 50 are provided in the annular ring 16, one of which islocated on either side of the portion 19. The passageways 50 are adaptedto receive an elutriating fluid, such as air, from a pressure sourcethereof. Although it should be understood that a variety of elutriatingfluids might be utilized in the present apparatus, air is preferred inthis embodiment and therefore, will be referred to as the elutriatingfluid throughout the remainder of this specification. Also, in thisembodiment pressurized air is utilized to produce a flow through thesystem, but it would be within the scope of this invention to use someother method to produce a pressure differential within the apparatus,such as vacuum producing means connected to conduit 46. An embodiment inwhich a vacuum producing means is connected to conduit 46 would notrequire an air tight cavity 17, that is the plates 13 and 14 wouldfunction only as supporting means for the annular ring 16. However, inthis embodiwardly from the outer most end of the fins 65. The aireventually passes through the fins 65, and out the conduits 36 and 46.The speed of the motor 57 is adjusted by rotating the rheostat controlknob 60 of rheostat 59 to provide a desired rotary speed of the rotor 12and separate any powders injected into the mechanism at a desired cutsize. Powder is injected into the chamber 33 through the conduit 73,solids inlet passageway 70, gap 28, and passageway 29.

As the powders enter the chamber 33, they are dispersed by the air alsoentering the chamber 33 along the periphery of the rotor 12. Therelatively narrow gap 28, between the rings 25 of the rotor 12 and theportion 19 of the housing 11 (see FIGS. 4 and creates a relatively highair velocity. This relatively high velocity air acts on the powders aslong as they remain in this area of the classifier to disperse thepowders into discrete particles. The rotor motion also creates atangential velocity component in and around the gap 29, and along thecenter inner edge of ring 19, resulting in a shear field that is alsoactive in dispersing the powders. Because the coarse fraction outletpassageway 72 is located a substantial distance forwardly, relative tothe direction of rotation of the rotor 12, of the solids inletpassageway 70 substantially of, the unclassified powders entering thesolids inlet passageway 70 are eventually dispersed as discreteparticles. The vortex then acts on each of the discrete particlesaccording to size and the particles larger than cut size are forcedoutwardly, while the particles smaller than cut size are carriedinwardly with the air. The large particles are carried through thecoarse fraction outlet passageway 72 and accumulated in the coarsefraction accumulating means 75. The fine particles are carried with theair through the conduits 36 and 46, and are separated from the air inthe fine fraction separating means 47. The fine fraction separatingmeans 47 is illustrated simply as a filtering bag, but it should beunderstood that any convenient method of separating the fine particlesfrom the air could be utilized.

Although this preferred embodiment only utilizes one solids inletpassageway 70 and one coarse fraction outlet passageway 72, it should beunderstood that a plurality of both passageways 70 and 72 might beutilized. Also, while an aspirating system is utilized to produce a flowin the coarse fraction outlet passageway 72, it should be understoodthat other methods might be utilized wherein a flow of air through thecoarse fraction accumulating means 75 is not necessary. For example, thecoarse fraction outlet passageway 72 might be slanted toward thedirection of rotation of the rotor 12 so that the coarse particles arenormally deflected therein.

While I have shown and described a specific embodiment of thisinvention, further modifications and improvements will occur to thoseskilled in the art. I desire it to be understood, therefore, that thisinvention is not limited to the particular form shown, and I intend inthe appended claims to cover all modifications which do not depart fromthe spirit and scope of this invention.

What is claimed is:

1. A centrifugal classifier comprising:

(a) a housing having an opening therein defining a generally cylindricalinner wall;

(b) a rotor mounted for rotation within the opening in said housing soas to form an annular gap between said rotor and the inner wall, saidrotor having an aperture therein in communication with said gap alongsubstantially the entire periphery of said rotor",

(0) means for rotating said rotor at a desired speed to produce a vortexin an elutriation zone at least partially in said aperture adjacent theperiphery of said rotor for separating solids in the elutriation zoneinto a coarse and fine fraction;

(d) fluid inlet passageway means in said housing, positioned to supplyan elutriating fluid to the axial outer extremity of the annular gap forproviding a flow of elutriating fluid through to the annular gap intothe aperture in said rotor for the formation of the vortex produced bysaid rotor;

(e) an opening in said rotor in communication with said aperture throughwhich the fluid and the fine fraction from the elutriation zoneegresses;

(f) a solids inlet pasageway in said cylindrical inner wall adapted tosupply solids to be classified to the elutriation zone; and

(g) a coarse fraction outlet passageway in said cylindrical inner wallof said housing in communication with said gap positioned forwardly ofsaid solids inlet passageway relative to the direction of rotation ofsaid rotor for receiving from the elutriation zone a coarse fraction ofsolids entering said solids inlet passageway.

2. A centrifugal classifier as set forth in claim I having in addition aplurality of generally radially outwardly extending fins attached to therotor within the aperture.

3. A centrifugal classifier as set forth in claim 1 wherein the coarsefraction outlet passageway is connected to a coarse fraction collectionsystem including aspirating means for producing a flow of fluid and thecoarse fraction from the aperture in the rotor, a fluid returnpassageway in communication with the gap between said rotor and thecylindrical inner wall and accumulating means in communication with saidcoarse fraction outlet passageway and said fluid return passageway forremoving the coarse fraction from the fluid flowing therethrough.

4. A centrifugal classifier as set forth in claim 1 including means forvarying the rotational speed of the rotor to vary the cut size of thesolids to be classified.

5. A centrifugal classifier as set forth in claim 1 wherein the rotor isconstructed of two side portions fixedly connected in a spaced apartrelationship to form the aperture therebetween.

6. A centrifugal classifier as set forth in claim 5 wherein the coarsefraction outlet passageway is positioned in the cylindrical inner Wallof said housing at approximately the transverse center thereof so as tobe located in the plane of the aperture between the two side portionsand on the opposite side of the gap therefrom.

7. A centrifugal classifier as set forth in claim 5 wherein the two sideportions of the rotor are constructed so that the space therebetweenadjacent the periphery is substantially reduced in size.

8. A centrifugal classifier comprising:

(a) a housing having an opening therein defining a generally cylindricalinner wall;

(b) a rotor mounted for rotation within the opening in said housing soas to form an annular gap between said rotor and the inner wall, saidrotor having an aperture therein extending radially outwardly intocommunication with said gap along substantially the entire periphery ofsaid rotor, said rotor having attached thereto within said aperture aplurality of generally radially outwardly extending fins, the outer endsof which are spaced from the periphery of said rotor;

(c) fluid inlet passageway means in said housing, positioned to supplyan elutriating fluid to the axial outer extremity of the annular gap forproviding a flow of elutriating fluid through the annular gap into theaperture in said rotor for the formation of the vortex produced by saidrotor;

(d) an axial opening in said rotor in communication with said aperturethrough which the fluid egresses;

(e) means for supplying an elutriating fluid to said fluid inletpassageway and for causing said fluid to flow through said aperture andegress through said axial opening;

(f) means for rotating said rotor at a desired speed to produce avortex, at least a portion of which vortex provides an elutriation zonebetween the ment the accumulating means 47 would have to be enclosed.

In FIGURE 1, the passageways 50 are connected to one end of a conduit 51and the other end is connected to a supply of pressurized air, notshown. A flow rate indicator 52 is interposed in the conduit 51 toindicate the fiow rate of the air during operation of the centrifugalclassifier. As air under pressure enters the passageways 50, the entirecavity 17 in the housing 11 is filled with pressurized air, which flowsthrough the gap 28 into the passageway 29 from both sides of the rotor12. In this embodiment, two passageways 50, one on either side of therotor 12, are provided to supply air equally to both sides of the gap28. The air flowing into the passageway 29 flows through the chamber 33in the rotor 12 and out the opening 35 into the conduit 36. The airegressing through the conduit 36 passes into the conduit 46 and the finefraction accumulating means 47 where it may be vented to the atmosphereor, in the case of a relatively expensive elutriating fluid, may bereturned to the pressure source.

Referring to FIGURES 1 to 3, the means for rotating the rotor 12 can beseen. The conduit 36 has a driven bevel gear 55 fixedly attached theretoin a coaxial relationship. Bevel gear 55 meshes with a driving bevelgear 56 which is attached for rotation with the rotor of a motor 57. Themotor 57 is mounted on a base 58 which is carried by and secured to asupporting surface. For the purpose of varying the speed of the motor57, and thus the shaft 36 which it drives, there is provided a rheostat59 operatively connected into the circuitry of the motor 57. Thus, theapparatus illustrated in FIG- URES 1 through 3 provides means forrotating the rotor and for varying the speed of rotation thereof. Itshould be understood that the above described apparatus for rotating therotor and varying the speed thereof is simply one device foraccomplishing that purpose, and many others will be obvious to thoseskilled in the art. Any and all apparatus for rotating the rotor andvarying the speed thereof come within the scope of this invention.

The rotor 12 has a plurality of radially extending fins 65 equallyspaced about the axis with the inner ends spaced from the axis of therotor 12. The outermost ends of the fins 65 are located at approximatelythe inner periphery of the annular rings 25. Thus, the fins 65 arespaced from the gap 28 approximately the radial dimension of the annularrings 25, and the opening between the annular rings 25 is free of anystructure. Applying air to the passageways 50 fills the cavity 17 in thehousing 11 and the air flows into the gap 28 from either side of therotor 12 and then into the passageway 29. Energizing the motor 57 causesthe rotor 12 to rotate at a predetermined speed, and the fins 65 in thechamber 33 of the rotor 12 produce a vortex at least a portion of whichis in an area between the annular rings 25 and the ends of the fins 65.The air forming the vortex passes between the fins 65 and egressesthrough the conduit 36. The fins 65 are utilized in the preferredembodiment because the substantially forced vortex produced therebyprovides more reliable control of classification. It will be understoodby those skilled in the art, however, that the fins 65 might beeliminated and a vortex will be formed during the operation due to dragon the air by the rotating surfaces of the rotor.

Referring to FIGURES 5, 6, and 7, three passageways in the annular ring16 of the housing 11 are illustrated. Referring to the passageways fromleft to right in FIG- URE 6, the first passageway is a solids inletpassageway designated 70. The second passageway adjacent the solidsinlet passageway 70, but spaced therefrom in a clockwise direction, isan air return passageway 71. The third passageway adjacent the airreturn passageway 71, but spaced therefrom in a clockwise direction, isa coarse fraction outlet passageway 72. Each of the passageways 70, 71,and 72 are positioned at approximately the trans- 6 verse or axialcenter of the annular ring 16 in the housing 11. Thus, the outlets ofeach of the passageways 70, 71, and 72 are in the plane of thepassageway 29 in the rotor 12, but spaced therefrom across the gap 28.In the present embodiment, the rotor 12 is adapted to turn in a counterclockwise direction, referring to FIGURE 6, so that the coarse fractionoutlet passageway 72 is spaced forwardly of the solids inlet passageway70 approximately 330 degrees with respect to the rotor 12 rotation, thatis, 330 degrees in a counter clockwise direction. The solids inletpassageway 70 has a feed line 73 attached thereto for transportingsolids, such as a powder to be classified, from a source to the solidsinlet passageway 70 and into the vortex in the chamber 33 of the rotor12. The vortex is formed at least partially in an elutriating zone inthe chamber 33 between the annular ring 16 of the housing 11 and theoutermost ends of the fins 65. The portion of the vortex in theelutriating zone separates the solids into a coarse fraction, which isforced outwardly toward the annular ring 16, and a fine fraction, whichis carried inwardly with the air between the fins 65 and into theconduit 36. Rings 25 are shaped to provide a transition for the gas fiowfrom the inner edge of gap 28 to the inner edge of the rotor plates 30and 33. In the present embodiment (see especially FIG. 5) this is shownas a radially inwardly expanding passageway 29, resulting in atriangular cross-section for the rings 25. This passageway 29, however,could have any variety of shapes.

One end of a conduit 74 is attached to the coarse fraction outletpassageway 72 through a T-junction 85 and the other end is attached tothe input of a coarse fraction accumulating means 75. The outlet of thecoarse fraction accumulating means 75 is attached to one end of aconduit 76, the other end of which is connected to an arm of aT-junction 77. The opposite arm of T-junction 77 is connected to one armof a T-junction 78 which has another arm connected to the air returnpassageway 71. The open arm of the T-junction 77 is connected through aconduit 79 to a flow rate indicator 80. The open arm. of the T-junction78 is connected through a conduit 81 to one arm of a T-junction 82 whichhas ,a flow rate indicator 83 connected in one arm, and a source of airunder pressure connected into the other arm. Thus, the conduit 81conducts air under pressure through the T- junction 78 which operates asan aspirator to draw air out of the coarse fraction accumulating means75. As the air is drawn out of the coarse fraction accumulating means75, air is drawn therein through the conduit 74 and the coarse fractionoutlet passageway 72 from the passageway 29. Air from the pressuresource in the conduit 81 and air drawn from the coarse fractionaccumulating means 75 returns to the passageway 29 through the airreturn passageway 71. Thus, a flow of air is provided into the coarsefraction accumulating means 75 which draws the coarse fraction from thepassageway 29 through the coarse fraction outlet passageway 72 and intothe coarse fraction accumulating means 75. A conduit 84 is connected tothe coarse fraction outlet passageway 72 by means of the T-junction 85and a flow rate indicator 86 is connected at the other end thereof sothat the flow rate at the coarse fraction outlet passageway 72 can becompared to the flow rate at the air return passageway 71. By comparingthe flow rates on the indicators and 86, an operator can determinewhether the coarse fraction outlet passageway 72 or the coarse fractionaccumulating means 75 is operating correctly.

In the operation of this preferred embodiment of the centrifugalclassifier, a source of air under pressure is supplied through theconduit 51 to the cavity 17 in the housing 11. This air passes into thegap 28 from either side of the rotor 12 and then into the chamber 33through the passageway 29. The rotor 12 is rotated at a predeterminedspeed by the motor 57 and the fins 65 in the chamber 33 produce a vortexat least partially in an elutriation zone located in the chamber 33radially outinner wall of said housing and the outer ends of said fins;

(g) a solids inlet passageway in said cylindrical inner wall positionedto supply solids to be classified to the elutriation zone;

(h) a coarse fraction outlet passageway in said cylindrical inner wallof said housing in communication with said gap and positioned forwardlyof said solids inlet passageway relative to the direction of rotation ofsaid rotor for receiving a coarse fraction from the elutriation zone;and

(i) means communicating with said opening in said rotor for receiving afine fraction from the elutriation zone.

9. A centrifugal classifier comprising:

(a) a housing having an opening therein defining a generally cylindricalinner wall;

(b) a rotor having an axial width smaller than the axial width of theinner wall of said housing and mounted for rotation within said housingso as to form an annular gap therebetween relatively narrow as comparedto the axial length thereof, said rotor having an aperture therein incommunication with said gap along substantially the entire periphery ofsaid rotor;

(c) means for rotating said rotor at a desired speed to produce a vortexin an elutriation zone in said aperture adjacent the periphery of saidrotor for separating solids in the elutriation zone into a coarse and afine fraction;

((1) fluid inlet passageway means in said housing, positioned to supplyan elutriating fluid to the axial outer extremity of the annular gap forproviding a flow of elutriating fluid through the annular gap into theaperture in said rotor for the formation of the vortex produced by saidrotor;

(e) axially extending conduit means fixedly attached to said rotor incommunication with said aperture through which the fluid and the finefraction from the elutriation zone egresses, said conduit meansextending outwardly through an opening in said hous- 2;

(f) fine fraction accumulating means in communication with said conduitmeans for receiving the fine fraction;

(g) sealing means between said conduit means and said housing andbetween said conduit means and said fine fraction accumulating means forallowing relative rotation therebetween while preventing the egress ofsolids;

(h) a solids inlet passageway in said cylindrical wall for supplyingsolids to be classified to the elutriation zone; and

(i) a coarse fraction outlet passageway in said cylindrical wall of saidhousing in communication with said gap positioned forwardly of saidsolids inlet passageway relative to the direction of rotation of saidrotor for receiving from the elutriation zone the coarse fraction ofsolids entering said solids inlet passageway.

10. A centrifugal classifier as set forth in claim 9 wherein the fluidinlet passageway means includes an inlet passageway extending throughthe housing at both sides of the rotor and adjacent the peripherythereof.

References Cited UNITED STATES PATENTS 2,367,906 1/1945 Wall 2091443,269,537 8/1966 Kaiser 209144 2,739,709 3/1956 Kaiser 209-144 3,089,5955/1963 Kaiser 209144 FOREIGN PATENTS 694,219 7/ 1953 Great Britain.1,007,440 10/ 1965 Great Britain.

FRANK W. LUTTER, Primary Examiner

